Field of the Invention
The invention relates to a data carrier with a coil for communication, i.e., for the contactless reception of data and energy and the contactless transmission of data. The data carrier has a logic circuit for processing and storing the received, demodulated, and decoded data.
Currently, such data carriers are used primarily as so-called contactless smart cards (chip cards), or, if in addition to the contactless interface they are also provided with terminal contacts, as so-called combination cards or dual interface cards. However, their use is not restricted to the form and shape of a card, since they have also already been proposed in wristwatches and hang tags, for instance for ski lifts.
In ISO Standard 14443 for the contactless interface of such smart cards, two different kinds of modulation for the data, transmitted from a read/write station to a card, are listed. These are pure blanking of the data carrier, which is also known as on-off keying and has the working title ASK100%, and Amplitude Shift Keying (ASK) modulation with a modulation depth of 5% to 15%, with the working title ASK10%. The terms "ASK10%" and "10%-ASK-modulated signals" as used herein refers to a type of modulation as defined by ISO Standard 14443.
Different kinds of bit coding are associated with these types of modulation. For instance, with ASK100%, pulse position coding is employed. The type of modulation and bit coding of the data, sent from a smart card to a read-write station, may also be different.
ASK100% has the advantage of being easy to demodulate, since all that is required is a blanking gap detection circuit. However, during the blanking gap, the clock pulse is missing, and relatively major sidebands occur in the frequency spectrum.
ASK10%, by comparison, makes a continuous clockline possible and entails a substantially lower level of sidebands but is difficult to demodulate, because on the one hand the distance between the card and the read-write station can fluctuate greatly, the circuits on the side of the card have a severely fluctuating current consumption, and the circuitry options for the demodulator circuit are limited, since no sufficiently constant, adequately high voltage supply is available.